Telecommunication providers in the United States are required by the Federal Communications Commission (“FCC”) to support 911 emergency call services. That is, when a telephone user dials 9-1-1, the telecommunication carrier must be able to process the call to determine the geographic location from where the call is originated to enable dispatching emergency personnel to the location of the 911 caller. In traditional public switched telephony networks (“PSTN”), the geographic information retrieval support for 911 is implemented by fixing associations between wireline telephone numbers and geographic street addresses. Telecommunication providers usually store a subscriber's location (e.g., a street address) in a database associated with an assigned telephone number (e.g., a call back number (“CBN”)) during the service activation. When a PSTN user makes a 911 call, the calling telephone number (i.e., the CBN) of the incoming 911 call can be used to look up the geographic location of the caller, and the retrieved location information can be used to dispatch emergency personnel to the caller.
The introduction of Voice over IP (“VoIP”) technology introduces various challenges to service providers to support 911 services. In particular, under a roaming service, a VoIP subscriber can easily disconnect a VoIP telephone from one location (e.g., the subscriber's home or workplace), connect the VoIP telephone in another location (e.g., a visited local area network (“LAN”), a coffee shop, a vacation spot, etc.), and register the VoIP telephone with the VoIP service provider to place telephone calls from the other location. This roaming capability of VoIP phones eliminates the dedicated or fixed association between telephone numbers and physical or geographic locations.